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Why This Chapter Matters

Human biology is arguably the most exam-friendly section in the entire General Awareness syllabus for RRB NTPC, because you already live inside the subject matter. Every organ system question, every disease question, every vitamin-deficiency question describes something happening in your own body right now. RRB and SSC papers consistently draw 5 to 8 questions from this territory: organ systems, diseases and their causes, vitamins and minerals, and immunity basics.

The biggest mistake aspirants make is treating vitamin names, deficiency diseases, and disease-causing organisms as three separate lists to cram independently, when they are really one connected story: a nutrient is missing, a specific consequence follows, and that consequence has a specific name. Learn the chain, not the fragments, and you will find you rarely forget which vitamin causes which deficiency disease, because the logic carries you there even when memory alone would fail.

The Digestive System

Digestion is the process of breaking down food into molecules small enough for the body to absorb and use for energy, growth, and repair. The digestive system is essentially a long tube running from mouth to anus, with several organs attached along the way to break food down chemically and mechanically.

Digestion starts in the mouth, where teeth mechanically crush food and saliva (containing the enzyme salivary amylase) begins breaking down starch chemically. This is why chewing rice for a while makes it taste faintly sweet: the amylase is already converting starch into simpler sugars in your mouth.

Food then travels down the oesophagus (food pipe) through rhythmic muscular contractions called peristalsis, a wave-like squeezing motion that pushes food along even if you were lying upside down; peristalsis, not gravity, is what actually moves food through your digestive tract.

The stomach churns food and adds gastric juice containing hydrochloric acid (which kills many ingested bacteria and activates digestive enzymes) and pepsin (which breaks down proteins). The stomach lining is protected from this strong acid by a thick layer of mucus; when this protective mucus layer is damaged, the acid attacks the stomach wall itself, causing a peptic ulcer.

The small intestine is where most digestion and nearly all nutrient absorption happens, and it is remarkably long, roughly 6 to 7 metres in an adult, coiled tightly to fit inside the abdomen. Three organs contribute digestive juices here: the liver produces bile (which does not digest fat chemically but emulsifies it, breaking large fat globules into smaller droplets for enzymes to act on more easily, similar to how dish soap breaks up grease into smaller manageable bits), the pancreas produces enzymes that digest carbohydrates, proteins, and fats, and the intestinal wall itself produces final enzymes that complete digestion. The inner surface of the small intestine is covered in finger-like projections called villi, which dramatically increase surface area for absorbing digested nutrients into the bloodstream.

The large intestine absorbs water and salts from the remaining undigested material, compacting it into solid waste, which is stored in the rectum before elimination through the anus.

Exam trap: Students often assume the liver produces digestive enzymes. It does not; the liver's digestive role is limited to producing bile, which is stored in the gall bladder before release into the small intestine. The pancreas is the organ that actually produces the bulk of digestive enzymes, alongside also producing the hormone insulin, giving it two very different jobs in the body.

Memory hook: Picture digestion as a factory assembly line: the mouth is the intake station (crushing raw material), the stomach is the churning vat (mixing with acid), the small intestine is the actual assembly line where every useful part gets extracted and shipped into the bloodstream, and the large intestine is the packaging and disposal unit for whatever is left over.

The Respiratory System

Breathing brings oxygen into the body and removes carbon dioxide, a waste product of cellular respiration. Air enters through the nose, where tiny hairs and mucus filter out dust and warm the incoming air, then passes down the trachea (windpipe), which branches into two bronchi, one for each lung, which further branch into smaller bronchioles, ending in tiny air sacs called alveoli.

Alveoli are where the actual gas exchange happens: oxygen passes from inhaled air into the blood, and carbon dioxide passes from the blood into the air to be exhaled. Human lungs contain hundreds of millions of alveoli, giving an enormous total surface area (often compared to roughly the size of a tennis court when spread flat) packed into a chest cavity, precisely because efficient gas exchange demands as much surface contact as possible between air and blood vessels.

Breathing itself is powered by the diaphragm, a dome-shaped muscle beneath the lungs. When you inhale, the diaphragm contracts and flattens, expanding the chest cavity and drawing air in; when you exhale, it relaxes back into its dome shape, pushing air out. This is why a hiccup, essentially an involuntary spasm of the diaphragm, causes that sudden gasping "hic" sound.

Exam trap: Do not confuse breathing (the physical movement of air in and out of lungs) with respiration (the chemical process at the cellular level that breaks down glucose using oxygen to release energy, producing carbon dioxide and water as byproducts). Breathing is mechanical; respiration is chemical, and it happens inside every living cell in your body, not just in the lungs.

The Circulatory System

The circulatory system transports blood, and with it oxygen, nutrients, hormones, and waste products, throughout the body. Its central organ is the heart, a muscular pump roughly the size of your closed fist, beating on average 60 to 100 times per minute in a healthy resting adult.

The human heart has four chambers: two upper chambers called atria (singular: atrium) and two lower chambers called ventricles. The right side of the heart handles deoxygenated blood (received from the body, sent to the lungs for oxygenation), while the left side handles oxygenated blood (received from the lungs, pumped out to the rest of the body). This is why the left ventricle has the thickest muscular wall of all four chambers: it must generate enough pressure to push blood through the entire body, a far bigger job than the right ventricle's short trip to the nearby lungs.

Blood itself has four main components. Red blood cells (RBCs), also called erythrocytes, carry oxygen using a protein called haemoglobin, which gives blood its red colour; RBCs are produced in bone marrow and have a lifespan of about 120 days. White blood cells (WBCs), or leukocytes, are the body's defence force, fighting infection; they are fewer in number than RBCs but increase sharply during infection, which is why a blood test showing elevated WBC count signals the body is fighting something. Platelets help blood clot, sealing wounds and preventing excessive bleeding. Plasma, the pale yellow liquid component, carries all of these cells along with dissolved nutrients, hormones, and waste products; plasma makes up over half of total blood volume.

Blood groups are classified mainly by the ABO system (types A, B, AB, and O) combined with the Rh factor (positive or negative), giving eight common blood group combinations. Karl Landsteiner discovered the ABO blood group system in 1901, a discovery that made safe blood transfusion possible for the first time by explaining why mismatched blood caused dangerous reactions. O-negative blood is often called the "universal donor" because it lacks the A, B, and Rh antigens that trigger immune reactions, making it broadly compatible in emergencies, while AB-positive is the "universal recipient," able to receive from all types because it already carries all the relevant antigens itself and will not react against them.

Blood pressure measures the force blood exerts against artery walls, recorded as two numbers: systolic pressure (the higher number, measured when the heart contracts and pumps) over diastolic pressure (the lower number, measured when the heart relaxes between beats). A commonly cited normal reading is around 120/80 mmHg. Hypertension (persistently high blood pressure) strains the heart and blood vessels over time, while hypotension refers to abnormally low blood pressure.

Memory hook: Remember the heart's blood flow direction with "Right side, blue and tired; Left side, red and fired." The right side receives tired, deoxygenated (conceptually "blue") blood and sends it to the lungs; the left side receives fresh, oxygenated ("red," energised, "fired up") blood from the lungs and pumps it out to fuel the whole body.

The Nervous System

The nervous system is the body's command and communication network, built from specialised cells called neurons that transmit electrical and chemical signals. It is divided into the central nervous system (CNS), consisting of the brain and spinal cord, and the peripheral nervous system, consisting of nerves that branch out to every part of the body.

The brain itself has three major parts tested repeatedly in exams. The cerebrum, the largest part, handles thinking, memory, voluntary movement, and sensory interpretation; it is divided into left and right hemispheres, each controlling movement and sensation on the opposite side of the body. The cerebellum, located below the cerebrum, coordinates balance, posture, and precise voluntary movements; damage here often shows up as clumsy, jerky, poorly coordinated movement rather than paralysis. The medulla oblongata, part of the brainstem connecting the brain to the spinal cord, controls involuntary, automatic functions essential to survival: heartbeat rate, breathing rate, and blood pressure.

Exam trap: Questions often ask which brain part controls a specific automatic function, like heartbeat or breathing, and offer "cerebrum" as a tempting wrong answer because it is the most commonly recalled brain part. The correct answer for automatic survival functions is almost always the medulla oblongata, not the cerebrum.

The spinal cord runs down the back inside the protective vertebral column and acts as the main communication highway between the brain and the rest of the body, also directly handling reflex actions: automatic, rapid responses that bypass the brain entirely for speed. Touching a hot object and instantly pulling your hand back happens through a reflex arc at the spinal cord level, faster than waiting for the signal to travel all the way to the brain and back; you only consciously register the pain a fraction of a second after your hand has already moved.

The Excretory System

Excretion removes metabolic waste products from the body, keeping the internal environment stable. The primary excretory organs are the kidneys, a pair of bean-shaped organs located toward the back of the abdomen. Each kidney contains roughly a million tiny filtering units called nephrons, which filter blood continuously, removing waste products (chiefly urea, produced from protein breakdown) while reabsorbing useful substances like water, glucose, and salts back into the blood.

Filtered waste, now called urine, travels from each kidney through a tube called the ureter to the urinary bladder, which stores urine until it is released through the urethra. Kidneys also play an essential role beyond simple filtration: they regulate the body's water and salt balance, help control blood pressure, and produce a hormone that stimulates red blood cell production in bone marrow.

Exam trap: Students sometimes assume sweating is the body's main excretory mechanism because it is the most visible. Sweat glands in the skin do remove some waste (small amounts of salts and urea) along with excess heat, but this is a minor, secondary role; the kidneys remain the primary excretory organs by a very wide margin.

Think of the kidneys as a strict security checkpoint at a building entrance, constantly screening everyone (blood) passing through: useful visitors (glucose, water, salts the body needs) are waved back in, while waste and troublemakers (urea, excess salts, toxins) are turned away and shown the exit (excreted as urine).

Common Diseases and Their Causes

Diseases are classified by their cause, and this classification matters enormously for exams, because treatment and prevention strategies differ completely depending on the type of causative agent.

Bacterial diseases are caused by bacteria, single-celled microorganisms, and are typically treated with antibiotics. Common bacterial diseases tested in exams include tuberculosis (caused by Mycobacterium tuberculosis, primarily affecting the lungs), cholera (caused by Vibrio cholerae, spread through contaminated water, causing severe diarrhoea and dehydration), typhoid (caused by Salmonella typhi, spread through contaminated food and water), pneumonia (can be bacterial or viral, causing lung inflammation), tetanus (caused by Clostridium tetani, entering through deep wounds, causing severe muscle stiffness and spasms), and leprosy (caused by Mycobacterium leprae, affecting skin and nerves).

Viral diseases are caused by viruses, which are far smaller than bacteria and cannot reproduce independently; they hijack the host's own cells to make copies of themselves, which is why antibiotics (designed to attack bacterial cell processes) have no effect on viral infections. Common viral diseases include common cold and influenza (flu), chickenpox and measles, dengue and chikungunya (both spread by Aedes mosquito bites), hepatitis (several types, some viral, affecting the liver), polio (affecting the nervous system, historically causing paralysis, now largely eliminated in India through vaccination), rabies (transmitted through the bite of an infected animal, almost always fatal once symptoms appear, which is why immediate post-bite treatment is critical), and COVID-19 (caused by the SARS-CoV-2 coronavirus).

Exam trap: A frequently tested pair is malaria versus dengue, both mosquito-borne but caused by entirely different organisms. Malaria is caused by a parasite (Plasmodium, a protozoan, not a bacterium or virus) transmitted by the female Anopheles mosquito. Dengue is caused by a virus transmitted by the Aedes aegypti mosquito (the same mosquito that spreads chikungunya and Zika). Exams frequently ask which mosquito or which type of organism causes each, and swapping these two is the single most common wrong answer students pick.

Deficiency diseases result not from any external organism, but from a lack of essential nutrients in the diet. These connect directly into the vitamins and minerals section below, since each deficiency disease has a specific missing nutrient behind it.

Fungal diseases, though less commonly tested, include ringworm and athlete's foot, both affecting skin, thriving in warm, moist conditions.

Memory hook: Sort disease-causing agents using "Better Vaccines Prevent Fatalities": Bacteria (treated with antibiotics), Virus (often prevented with vaccines, since antibiotics do not work), Parasite (like malaria, treated with specific antiparasitic drugs), Fungus (treated with antifungal medication). Four categories, four different treatment logics, one sentence to keep them separate under exam pressure.

Vitamins and Minerals

Vitamins are organic compounds the body needs in small amounts for normal growth and function, and critically, the body cannot produce most of them on its own; they must come from diet (with the notable exceptions of Vitamin D, which the skin synthesises using sunlight, and Vitamin K, which gut bacteria partially produce). Each vitamin has a letter name, a specific function, common food sources, and a specific deficiency disease, and exams test all four angles.

Vitamin A (retinol) supports vision, especially night vision, and skin health. Sources include carrots, milk, egg yolk, and green leafy vegetables. Deficiency causes night blindness and, in severe cases, a condition called xerophthalmia affecting the cornea.

Vitamin B-complex is actually a group of several distinct vitamins, not one single vitamin, each with its own role. Vitamin B1 (thiamine) deficiency causes beriberi, affecting nerves and the heart. Vitamin B2 (riboflavin) deficiency causes cracked lips and skin issues. Vitamin B3 (niacin) deficiency causes pellagra, marked by skin, digestive, and mental symptoms. Vitamin B12 (cobalamin), found almost exclusively in animal products (a genuinely important fact for vegetarians and vegans to know), is essential for red blood cell formation and nerve function; deficiency causes a type of anaemia and nerve damage.

Vitamin C (ascorbic acid) supports immune function and wound healing, and crucially, is essential for collagen production (collagen holds skin, blood vessels, and connective tissue together). Sources include citrus fruits, amla (Indian gooseberry, exceptionally rich in Vitamin C), and green vegetables. Deficiency causes scurvy, historically a major problem for sailors on long voyages without fresh fruit, causing bleeding gums, loose teeth, and poor wound healing.

Vitamin D supports calcium absorption and bone health, and uniquely among vitamins, the body can produce it itself through skin exposure to sunlight. Deficiency causes rickets in children (soft, weak, deformed bones) and osteomalacia in adults (bone softening).

Vitamin E acts as an antioxidant, protecting cells from damage, and supports reproductive health; sources include nuts, seeds, and vegetable oils.

Vitamin K is essential for blood clotting; without it, even minor wounds would bleed excessively. Sources include green leafy vegetables, and the body's own gut bacteria contribute some supply.

Memory hook: Link each vitamin letter to its deficiency disease through a short story chain: "A man went night fishing and went blind (Vitamin A, night blindness). His legs grew weak from beri-beri disease as he struggled on the boat (B1, beriberi). Back home, his gums bled like a scurvy pirate's (C, scurvy). His bones went soft like rickety old furniture (D, rickets)." Odd, vivid, and precisely the kind of chain that survives exam-hall stress far better than a flat list.

Minerals are inorganic elements the body needs in smaller quantities but which are equally essential. Calcium builds and maintains bones and teeth, and is also needed for muscle function and blood clotting; dairy products are the classic source. Iron is essential for haemoglobin production; deficiency causes iron-deficiency anaemia, the most common nutritional deficiency worldwide, marked by fatigue and pale skin, and is a particular concern for pregnant women and growing children. Iodine is essential for thyroid hormone production; deficiency causes goitre (an enlarged thyroid gland, visible as swelling in the neck) and, if it happens during pregnancy or early childhood, can impair mental development, which is exactly why iodised salt became a major public health intervention across India. Sodium and potassium regulate fluid balance and are essential for nerve signal transmission. Zinc supports immune function and wound healing.

Exam trap: Iodine deficiency and iron deficiency both cause visible, testable symptoms, but for entirely different reasons, and questions sometimes swap the associated disease. Iron deficiency causes anaemia (fatigue, pale skin, weakness, low haemoglobin). Iodine deficiency causes goitre (thyroid swelling in the neck). Keep the organ connection straight: iron relates to blood (haemoglobin), iodine relates to the thyroid gland.

Vaccines and Immunity Basics

Immunity is the body's ability to resist and fight disease-causing organisms. It comes in two broad forms. Innate immunity is the immediate, general defence you are born with: physical barriers like skin and mucus, and general-purpose white blood cells that attack any invader without needing prior exposure. Acquired (adaptive) immunity develops over your lifetime as the body encounters specific pathogens and learns to recognise them, building targeted defences called antibodies against that specific threat.

Acquired immunity itself splits into two paths. Natural immunity develops when you are actually infected by a disease and your body fights it off, remembering that pathogen afterward. Artificial immunity develops through vaccination, deliberately introducing a weakened, inactivated, or partial form of a pathogen (or, in newer vaccine technology, genetic instructions for making a piece of it) into the body, training the immune system to recognise and remember it without causing the actual disease.

Think of vaccination as a fire drill: you are not lighting a real fire, but your body practises the exact response it would need for a real fire, so that when an actual outbreak (infection) happens, the response is fast and well-rehearsed rather than caught off guard.

Edward Jenner, an English physician, is widely credited as the pioneer of vaccination, developing the smallpox vaccine in 1796 after observing that milkmaids who had caught the mild disease cowpox seemed protected from the far more dangerous smallpox. This observation, and Jenner's experiment building on it, launched the entire field of immunology, and the very word "vaccine" comes from vacca, Latin for cow, in tribute to that cowpox origin.

Herd immunity is the protective effect that occurs when a large enough proportion of a population becomes immune to a disease (through vaccination or prior infection), making it hard for the disease to spread even to those who are not individually immune, indirectly protecting vulnerable people who cannot be vaccinated for medical reasons, such as newborns or those with certain health conditions.

India's Universal Immunization Programme provides vaccines against several serious childhood diseases free of cost, including tuberculosis (BCG vaccine), polio, diphtheria, pertussis (whooping cough), tetanus, measles, hepatitis B, and others, and this program is credited with India being declared polio-free (a landmark public health achievement, with the WHO certifying the South-East Asia region, including India, polio-free in 2014 after sustained decades-long vaccination efforts).

Exam trap: Do not confuse a vaccine (given before infection, to prevent disease by training immunity in advance) with treatment or antitoxin (given after infection or exposure, to counter a disease or toxin already present, such as anti-rabies treatment given promptly after a dog bite, or an antivenom given after a snakebite). Vaccines are preventive; antitoxins and antivenoms are typically reactive, given after exposure has already occurred.

Quick Revision — One-Line Facts

• Salivary amylase in saliva begins starch digestion in the mouth.
• Peristalsis, not gravity, moves food through the digestive tract.
• Bile is produced by the liver, stored in the gall bladder, and emulsifies fat.
• The pancreas produces both digestive enzymes and the hormone insulin.
• Villi in the small intestine increase surface area for nutrient absorption.
• Gas exchange in the lungs happens in tiny air sacs called alveoli.
• The diaphragm is the main muscle powering breathing.
• Breathing is mechanical; respiration is the chemical process releasing energy inside cells.
• The heart has four chambers: two atria and two ventricles.
• The left ventricle has the thickest wall because it pumps blood to the entire body.
• RBCs carry oxygen using haemoglobin and live about 120 days.
• WBCs fight infection; platelets help blood clot; plasma is the liquid carrier component.
• Karl Landsteiner discovered the ABO blood group system in 1901.
• O-negative blood is the universal donor; AB-positive is the universal recipient.
• Normal blood pressure is commonly cited as around 120/80 mmHg.
• The cerebrum handles thinking and voluntary movement; the cerebellum handles balance and coordination.
• The medulla oblongata controls involuntary functions like heartbeat and breathing.
• Reflex actions are processed at the spinal cord level for faster response.
• Kidneys filter blood through roughly a million nephrons each, removing urea as urine.
• Sweat removes only minor waste; kidneys are the primary excretory organs.
• Malaria is caused by a Plasmodium parasite spread by female Anopheles mosquitoes.
• Dengue is caused by a virus spread by Aedes aegypti mosquitoes.
• Antibiotics work against bacteria, not viruses.
• Vitamin A deficiency causes night blindness; Vitamin C deficiency causes scurvy.
• Vitamin D deficiency causes rickets in children and osteomalacia in adults.
• Vitamin B1 deficiency causes beriberi; Vitamin K is essential for blood clotting.
• Iron deficiency causes anaemia; iodine deficiency causes goitre.
• Edward Jenner developed the smallpox vaccine in 1796, the first vaccine.
• Herd immunity protects unvaccinated individuals when enough of a population is immune.
• India, along with the rest of the WHO South-East Asia region, was certified polio-free in 2014.

Memory Tables

Table 1: Vitamins, Deficiency Diseases, and Key Sources

Vitamin	Deficiency Disease	Key Source
Vitamin A	Night blindness	Carrots, milk, green leafy vegetables
Vitamin B1	Beriberi	Whole grains, legumes
Vitamin B3	Pellagra	Meat, groundnuts, whole grains
Vitamin B12	Anaemia, nerve damage	Animal products (meat, milk, eggs)
Vitamin C	Scurvy	Citrus fruits, amla, green vegetables
Vitamin D	Rickets (children), osteomalacia (adults)	Sunlight, fish, fortified milk
Vitamin K	Poor blood clotting	Green leafy vegetables, gut bacteria

Table 2: Disease-Causing Organisms and Examples

Type of Agent	Example Diseases	Typical Treatment
Bacteria	Tuberculosis, cholera, typhoid, tetanus	Antibiotics
Virus	Dengue, measles, polio, common cold, COVID-19	Antivirals/supportive care, prevention via vaccines
Parasite	Malaria	Antiparasitic drugs
Fungus	Ringworm, athlete's foot	Antifungal medication
Nutrient deficiency	Scurvy, rickets, goitre, anaemia	Dietary correction/supplements

Practice MCQs

Q1. Which organ produces bile, which is later stored in the gall bladder? (a) Pancreas (b) Liver (c) Stomach (d) Small intestine

Q2. The wave-like muscular contraction that moves food through the digestive tract is called: (a) Digestion (b) Peristalsis (c) Absorption (d) Excretion

Q3. Gas exchange in the lungs occurs in structures called: (a) Bronchi (b) Trachea (c) Alveoli (d) Diaphragm

Q4. Which chamber of the heart has the thickest muscular wall? (a) Right atrium (b) Left atrium (c) Right ventricle (d) Left ventricle

Q5. Who discovered the ABO blood group system? (a) Edward Jenner (b) Karl Landsteiner (c) Louis Pasteur (d) Alexander Fleming

Q6. Which blood group is commonly known as the universal donor? (a) AB-positive (b) A-positive (c) O-negative (d) B-negative

Q7. Which part of the brain controls involuntary functions such as heartbeat and breathing? (a) Cerebrum (b) Cerebellum (c) Medulla oblongata (d) Spinal cord

Q8. The primary excretory organs responsible for filtering blood and forming urine are the: (a) Lungs (b) Kidneys (c) Liver (d) Skin

Q9. Malaria is caused by which type of organism? (a) Virus (b) Bacteria (c) Parasite (Plasmodium) (d) Fungus

Q10. Dengue fever is transmitted by which mosquito? (a) Female Anopheles (b) Aedes aegypti (c) Culex (d) Male Anopheles

Q11. Deficiency of Vitamin C leads to which disease? (a) Rickets (b) Beriberi (c) Scurvy (d) Night blindness

Q12. Which vitamin does the human body synthesise on its own through sunlight exposure? (a) Vitamin A (b) Vitamin C (c) Vitamin D (d) Vitamin B12

Q13. Iodine deficiency in the diet primarily leads to: (a) Anaemia (b) Goitre (c) Scurvy (d) Rickets

Q14. Who is credited with developing the first vaccine, against smallpox, in 1796? (a) Louis Pasteur (b) Edward Jenner (c) Robert Koch (d) Alexander Fleming

Q15. Antibiotics are effective against which type of disease-causing agent? (a) Viruses (b) Bacteria (c) Nutrient deficiencies (d) All disease agents equally

Answer Key

Q	Answer	Reason
1	(b) Liver	The liver produces bile, which is stored in the gall bladder and released to emulsify fats.
2	(b) Peristalsis	These rhythmic muscular waves push food along the tract regardless of body position.
3	(c) Alveoli	These tiny air sacs provide the large surface area needed for oxygen and carbon dioxide exchange.
4	(d) Left ventricle	It pumps blood to the entire body, requiring far more force than the right ventricle's short trip to the lungs.
5	(b) Karl Landsteiner	His 1901 discovery of the ABO system made safe blood transfusion possible.
6	(c) O-negative	It lacks A, B, and Rh antigens, making it broadly compatible across recipients in emergencies.
7	(c) Medulla oblongata	This brainstem structure controls automatic survival functions, distinct from the cerebrum's role in conscious thought.
8	(b) Kidneys	Kidneys filter blood through nephrons; sweat glands play only a minor secondary excretory role.
9	(c) Parasite (Plasmodium)	Malaria is caused by a protozoan parasite, not a virus, unlike the commonly confused dengue.
10	(b) Aedes aegypti	This mosquito, distinct from the Anopheles that spreads malaria, also transmits chikungunya.
11	(c) Scurvy	Vitamin C deficiency causes scurvy, marked by bleeding gums and poor wound healing.
12	(c) Vitamin D	Skin exposed to sunlight synthesises Vitamin D, unlike other vitamins that must come entirely from diet.
13	(b) Goitre	Iodine deficiency impairs thyroid hormone production, causing the gland to enlarge visibly in the neck.
14	(b) Edward Jenner	His 1796 smallpox vaccine, based on cowpox exposure in milkmaids, founded modern immunology.
15	(b) Bacteria	Antibiotics target bacterial cell processes and have no effect on viruses, parasites, or nutrient deficiencies.